Eyepiece for Virtual, Augmented, or Mixed Reality Systems

1. An eyepiece for a virtual reality, augmented reality, or mixed reality system, the eyepiece comprising: first and second waveguide substrates that are at least partially transparent; an input coupler grating formed on or in each of the first and second waveguide substrates and configured to couple at least one respective input light beam that is externally incident on the input coupler grating into at least a respective first guided light beam that propagates inside the respective first and second waveguide substrates; a first orthogonal pupil expander (OPE) grating formed on or in each of the first and second waveguide substrates and configured to divide the respective first guided light beam from the respective input coupler grating into a respective plurality of parallel, spaced-apart light beams; and an exit pupil expander (EPE) grating formed on or in each of the first and second waveguide substrates and configured to re-direct the respective light beams from the respective first OPE grating such that they exit the respective first and second waveguide substrates, the EPE grating comprising a plurality of curved lines whose curvature determines an amount of optical power of the EPE grating, wherein the first and second waveguide substrates are configured to respectively output a plurality of output beams such that they correspond to different respective first and second depth planes, the first and second depth planes being determined by the respective optical powers of the EPE grating of the first waveguide substrate and the EPE grating of the second waveguide substrate, the EPE grating of the second waveguide substrate comprising an amount of optical power that is different than the optical power of the EPE grating of the first waveguide substrate.

2. The eyepiece of claim 1 , wherein the first waveguide substrate is less than 325 microns thick.

3. The eyepiece of claim 1 , wherein the first waveguide substrate comprises glass, plastic, or polycarbonate.

4. The eyepiece of claim 1 , wherein the first waveguide substrate is configured to project a color component of image data.

5. The eyepiece of claim 1 , further comprising a projector to direct light toward the input coupler grating of the first waveguide substrate and toward the input coupler grating of the second waveguide substrate.

6. The eyepiece of claim 1 , wherein the input coupler grating is configured to divide and re-direct the at least one input light beam that is externally incident on the input coupler grating into first and second guided light beams that propagate inside the first waveguide substrate, the first eyepiece waveguide further comprising: a second OPE grating formed on or in the substrate and configured to divide the second guided light beam from the input coupler grating into a plurality of parallel, spaced-apart light beams, wherein the EPE grating is configured to re-direct the light beams from the first and second OPE gratings such that they exit the first waveguide substrate, and wherein the input coupler grating is positioned between the first OPE grating and the second OPE grating and is configured to direct the first guided light beam toward the first OPE grating and to direct the second guided light beam toward the second OPE grating.

7. The eyepiece of claim 6 , wherein the input coupler grating is configured to separate the input light beam into a +1 diffractive order directed toward the first OPE grating and a −1 diffractive order directed toward the second OPE grating.

8. The eyepiece of claim 6 , wherein the first and second OPE gratings are separated by approximately 180° and the EPE grating is located at about 90° to both OPE gratings.

9. The eyepiece of claim 6 , wherein the first and second OPE gratings are slanted toward the EPE grating.

10. The eyepiece of claim 9 , wherein the first and second OPE gratings are separated by approximately 120° and the EPE grating is located at about 60° to both OPE gratings.

11. The eyepiece of claim 6 , wherein the input coupler grating comprises diffractive optical features to divide and redirect the input light beam toward the first and second OPE gratings.

12. The eyepiece of claim 11 , wherein the diffractive optical features of the input coupler grating comprise a plurality of lines forming at least one diffraction grating.

13. The eyepiece of claim 11 , wherein the diffractive optical features of the input coupler grating comprise a plurality of features laid out on in a lattice pattern.

14. The eyepiece of claim 13 , wherein the lattice pattern comprises a hexagonal lattice.

15. The eyepiece of claim 11 , wherein the diffractive optical features of the input coupler grating comprise a crossed grating.

16. The eyepiece of claim 11 , wherein the diffractive optical features of the input coupler grating are configured to direct light toward the first and second OPE gratings, and toward the EPE grating without first passing through either of the OPE gratings.

17. The eyepiece of claim 6 , wherein the first and second OPE gratings comprise diffractive optical features to divide each of the first and second guided light beams into the plurality of parallel, spaced-apart light beams.

18. The eyepiece of claim 17 , wherein the diffractive optical features of the first and second OPE gratings comprise a plurality of lines forming diffraction gratings.

19. The eyepiece of claim 18 , wherein the diffraction gratings of the first and second OPE gratings are angled so as to direct the plurality of spaced-apart light beams toward the EPE grating.

20. The eyepiece of claim 6 , wherein the first waveguide substrate further comprises: a first spreader grating that receives the light beams from the first OPE grating and spreads their distribution so as to reach a larger portion of the EPE grating; and a second spreader grating that receives the light beams from the second OPE grating and spreads their distribution so as to reach a larger portion of the EPE grating.

21. The eyepiece of claim 20 , wherein the first spreader grating and the second spreader grating are both configured to spread the distribution of the light beams toward the center of the EPE grating.

22. The eyepiece of claim 20 , wherein the first and second spreader gratings comprise diffractive optical features.

23. The eyepiece of claim 22 , wherein the diffractive optical features of each of the first and second spreader gratings comprise a plurality of lines that form diffraction gratings.

24. The eyepiece of claim 23 , wherein the diffraction grating of the first spreader grating is oriented at approximately 90° to a diffraction grating of the first OPE grating, and wherein the diffraction grating of the second spreader grating is oriented at approximately 90° to a diffraction grating of the second OPE grating.